JPH0227137B2 - - Google Patents

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a thermoplastic resin sheet (hereinafter simply referred to as a resin sheet) containing fibers of a low-melting point metal or alloy (hereinafter simply referred to as a low-melting point metal), and the resin sheet. The present invention relates to a method for producing a thermoplastic resin molded article (hereinafter simply referred to as a resin molded article) containing fibers of a low melting point metal obtained by thermoforming a sheet or a laminate thereof.

Due to the rapid spread of digital electronic devices in recent years and the use of plastic for their housings, electromagnetic interference has become a problem in which noise generated during operation of digital electronic devices adversely affects other digital electronic devices. As a method for producing electromagnetic shielding materials to prevent electromagnetic interference, a technique that imparts electrical conductivity to a plastic base material is attracting attention.

Since the resin sheets and resin molded products obtained by the method of the present invention contain fibers of low melting point metals with a high aspect ratio, they exhibit a high degree of conductivity.
As a technology for imparting electrical conductivity to plastic materials, it can be applied to a wide range of fields including materials for electronic devices such as electromagnetic shielding materials.

[Conventional technology]

To date, the manufacturing technologies for electromagnetic shielding materials based on plastic that have been proposed or implemented include zinc spraying, conductive paint, metal vapor deposition,
Surface treatment methods such as chemical plating, fine fibers, particles, etc. of conductive materials such as plastics and metals,
There is a method of making a composite material by mixing it with flakes or the like.

Also, conductive polymers have been proposed in which the plastic itself exhibits conductivity due to its special chemical structure.

However, some problems remain in all methods, including those currently in practical use.

[Problem that the invention seeks to solve]

Generally, electromagnetic shielding materials are required to stably exhibit a high degree of conductivity.

Zinc spraying has traditionally been the most common conductivity imparting technology because it provides a good shielding effect at a relatively low cost, but the problem is that the sprayed layer peels off due to poor adhesion between the plastic surface and the sprayed layer. In addition to problems such as deterioration of performance over time and circuit destruction of electronic devices, above all, the working environment deteriorates significantly during zinc spraying, so it is desirable to use other methods as an alternative. ing.

Conductive paint can impart conductivity to plastic molded objects by spray painting in the same way as conventional methods, but this spray painting is carried out smoothly and the thin film of paint formed on the plastic surface is highly conductive. In order to prevent the performance from deteriorating over time, it is necessary to add very fine fillers such as nickel or precious metals that do not easily oxidize, or copper or aluminum that has undergone special oxidation prevention treatment to the binder. However, since the technology to supply metal filler with such performance at low cost and in large quantities has not yet been established, conductive paint itself has not yet become widely used. .

Metal evaporation requires expensive equipment and multiple steps, making it unsuitable for mass production. Chemical plating is in the same situation as metal evaporation, and there are still problems such as the resins that can be used are limited. ing.

All techniques for imparting conductivity to plastic molded objects through surface treatment involve secondary processing to form a conductive thin layer on the plastic surface. Composite materials obtained by mixing conductive materials have the conductive materials dispersed in the plastic, so compared to cases where the conductive layer appears on the surface of the plastic, there is less chance of performance degradation due to destruction or oxidation of the conductive layer. There is less worry about negative effects on electronic devices due to deterioration or peeling of the conductive layer.

However, in the case of composite materials, the conductive material is dispersed throughout the plastic, so in order to impart a high degree of conductivity, it is necessary to add a large amount of conductive material compared to surface treatment. be.

However, when conductive fine fibers or fillers are added to plasticized plastics, the apparent viscosity of the plastic composition increases rapidly as the amount added increases. This not only makes it difficult to uniformly disperse the conductive material into the plastic during processes such as kneading, but also increases the shear force acting on the conductive material when kneading is strengthened to achieve uniform dispersion. , the destruction of the conductive material becomes noticeable, and the aspect ratio of fine metal fibers and the like is significantly lowered, so that the expected effect of imparting conductivity cannot be obtained in many cases.

In addition, fine metal fibers and carbon fibers, which have a large effect on imparting conductivity, have low productivity and are expensive materials, so composite materials containing these conductive materials are also used as general-purpose plastics, just as in the case of conductive paints. It becomes quite expensive in comparison.

Furthermore, research is currently underway to find a conductive polymer that exhibits electrical conductivity due to the special chemical structure of the plastic itself, and that is conductive enough to be used in electromagnetic shielding materials and that is affordable enough for general use. It is.

The present invention provides a manufacturing method that can supply a plastic material exhibiting high conductivity at a low cost due to the special nature of the method.

[Means to solve the problem]

In the present invention, a plurality of pores are provided in front of the die slit of an extrusion die for injecting molten low-melting point metal, and thermoplastic resin heated to a temperature higher than the melting point of the low-melting point metal to be used is injected into the die. While continuously injecting the molten low melting point metal through the pores into the thermoplastic resin flux, fibers of the molten low melting point metal having a very high aspect ratio are formed in the thermoplastic resin flux. A method for producing a resin sheet obtained by extruding it while forming a shaped body, and then cooling it while taking it out to form fibers of a low melting point metal in a thermoplastic resin, and a resin sheet or the like. This is a method for producing a resin molded product obtained by heating a laminate to a temperature equal to or higher than the melting point of a low-melting point metal and performing heat molding such as press molding, vacuum molding, or pressure molding.

The thermoplastic resin used in the present invention is not particularly limited as long as it can be used in ordinary extrusion molding and thermoforming. Such thermoplastic resins include, for example, polyolefins, polystyrenes, polyvinyl chloride, polyacrylates, polymethacrylates, polyacrylonitrile, polybutadiene, polyamides, polyesters, or modified products thereof; Examples include copolymers and mixtures. These thermoplastic resins can be selected depending on the moldability and physical property requirements of the molded product. Furthermore, in order to improve the affinity between the thermoplastic resin and the low melting point metal, an ionomer resin can be blended. Blending the ionomer resin in an amount of 5 parts by weight or more provides a great effect. Further, additive aids such as antioxidants, stabilizers, plasticizers, and lubricants may be added to these resin compositions as necessary.

The low melting point metal used in the present invention is one having a melting point below the temperature at which extrusion molding and heat molding of thermoplastic resins can be performed, that is, below 400°C, such as tin,
Examples include single substances or alloys of lead, zinc, bismuth, cadmium, antimony, etc.

[Effect]

The method for manufacturing a resin sheet according to the present invention will be further explained with reference to FIGS. 1 and 2.

A thermoplastic resin heated to a temperature higher than the melting point of the low melting point metal is injected into a die by an extruder. At this time, as shown in Figure 1, the thermoplastic resin is injected in multiple fluxes 1 from multiple injection ports as in normal multilayer extrusion molding, or as shown in Figure 2, the thermoplastic resin is heated in an extrusion die. After once dividing the flux 1 of the plastic resin, the flux 1 of the thermoplastic resin is divided into the die slits 3 of a plurality of pores 2 for injection of molten low-melting point metal in both cases of FIGS. 1 and 2. All you have to do is merge them.
At the point where the thermoplastic resins meet, a pump having a heat-resistant structure continuously injects molten low-melting point metal 6 into the thermoplastic resin 5 through a plurality of pores 2.

Due to the high viscosity of plasticized thermoplastics,
Molten low melting point metal 6 injected into thermoplastic resin 5
is supported in a thermoplastic resin and forms a fibrous shape with a high aspect ratio without contacting the inner surface of the die or the molten low melting point metal.

Furthermore, by cooling the heated thermoplastic resin composition while taking it, the molten low melting point metal is cooled and solidified to become a low melting point metal fiber having a high aspect ratio, and a resin sheet 4 is obtained.

A resin sheet or a laminate of resin sheets obtained by heat-pressing the resin sheet is heated to a temperature higher than the melting point of a low-melting point metal, and then heat-formed by press molding, vacuum forming, pressure forming, etc. A resin molded article can be produced using the same method.

Since the low melting point metal contained in the resin sheet or laminate is in a molten state during heat molding,
During the molding process, the fibrous shape of the low-melting point metal deforms as the plasticized resin sheet or laminate deforms, but it is not cut in the resin sheet or laminate and remains at a high aspect ratio. It is supported while maintaining the ratio.

In addition, in this thermoforming process, the thermoplastic resin and low melting point metal that make up the resin sheet or laminate are both plasticized or melted, so it is possible to Since the apparent viscosity of the plasticized thermoplastic resin does not increase, the resin sheet or laminate exhibits good moldability, and resin molded products of various shapes with excellent appearance can be manufactured. .

Example 1 ABS resin (JSR ABS38) 95 parts by weight Ionomer resin (Himilan 1652) 5 parts by weight Lead stearate 0.1 parts by weight of a resin composition was heated to resin temperature using a 40 mmφ extruder.
After heating to 200℃ and plasticizing, extrusion dies (Dice slit 0.4cm x 20cm x 3) kept at 200℃.
cm), a lead-tin alloy (melting point 185 °C) into the resin flux inside the die using a pump and extruding it together with the resin, and then cooling the resin sheet with two rolls and taking it off at a take-up speed of 12 m/min.
A resin sheet containing a lead-tin alloy was created.

The resin sheet after collection is approximately 22cm wide and 2.5mm thick.
In the continuous sheet, lead-tin alloy fibers with a diameter of 1.3 mm were running in the direction in which the resin sheet was taken. The fibers of this lead-tin alloy were supported in the continuous resin sheet without being cut, and had a very high aspect ratio.

A 10 cm x 10 cm plate-shaped sample was cut from any part of this continuous sheet, and the specific resistance of this sample in the direction in which the lead-tin alloy fibers ran was determined to be 10 ^-1
It was less than Ω-cm.

Example 2 From the continuous body of resin sheet described in Example 1, 20
A sample measuring cm x 20 cm was cut out and formed under pressure at a temperature of 200°C to create a box-shaped resin molding with a depth of 5 cm and a bottom of 15 cm x 15 cm.

The walls of this resin molding contain lead-tin alloy fibers with a diameter of 1 to 1.3 mm, and as a result of measuring the specific resistance in the direction in which the lead-tin alloy fibers travel, it was found that the resin sheet before molding Similarly, it was less than 10 ^-1 Ω-cm.

Example 3 Samples of 20 cm x 20 cm were cut from the continuous resin sheet described in Example 1 in the same manner as in Example 2, and two of the samples were cut so that the running directions of the lead-tin alloy fibers each contained were perpendicular to each other. A laminate with a thickness of 3 cm was formed by hot pressing at 180°C, and then heated to 200°C and pressure-formed in the same manner as in Example 2 to form a laminate with a depth of 5 cm.
A box-shaped resin molded product with a bottom size of 15 cm x 15 cm was created.

The walls of this resin molding contain lead-tin alloy fibers with a diameter of 1 to 1.3 mm in a lattice pattern, and as a result of measuring the specific resistance of the orthogonal lead-tin alloy fibers in the running direction, the molding 10 ^-1 Ω−cm like the previous resin sheet
It was below.

〔Effect of the invention〕

The production of resin sheets and resin molded products according to the present invention can be performed using ordinary thermoplastic resins without using special conductive materials such as metal fine fibers, which were conventionally required to impart conductivity to resin compositions. It is possible to directly subject low melting point metals to forming processes. Therefore, the present invention can eliminate the steps of manufacturing conductive materials such as metal fine fibers and particles or carbon fibers, and kneading these conductive materials with thermoplastic resin, resulting in higher production efficiency compared to conventional methods. It can be said that this technology can provide a method and product for manufacturing conductive resin molded products that are both highly economical and practical.

[Brief explanation of drawings]

FIG. 1 shows an example of a multilayer extrusion molding die used in the present invention, and is a schematic cross-sectional view of a resin sheet extrusion molding die provided with pores for molten metal injection.
FIG. 2 shows a die used in an embodiment of the present invention, and is a schematic cross-sectional view of a resin sheet extrusion molding die in which a molten metal injection device having a pore in a pipe is installed inside the extrusion molding die. In the drawings 1...Resin channel, 2...Pore for molten metal injection, 3...Dice slit, 4...Resin sheet, 5...Thermoplastic resin, 6...Low melting point metal, 7
... Molten metal injection equipment.

Claims (1)

[Claims] 1. In extrusion molding of a thermoplastic resin, a plurality of molten metals or alloys provided in a die are introduced into a flux of the thermoplastic resin heated to a temperature higher than the melting point of the metal or alloy. A method for producing a thermoplastic resin sheet containing fibers of a low melting point metal obtained by extrusion molding while continuously injecting through individual pores. 2. By thermoforming a thermoplastic resin sheet containing fibers of a low melting point metal according to claim 1 under conditions of a temperature equal to or higher than the melting point of the low melting point metal or alloy contained in the resin sheet. A method for producing a thermoplastic resin molded article containing fibers of a low melting point metal obtained by 3. Heat-forming a laminate of thermoplastic resin sheets containing fibers of a low melting point metal according to claim 1 under conditions of a temperature equal to or higher than the melting point of the low melting point metal or alloy contained in the resin sheet. A method for producing a thermoplastic resin molded article obtained by.